Mesh networking tackles in-plant obstacles

How to provide robust sensor communications despite power limitations and lots of radio frequency interference

“If we’re going to have smart things, then we need smart networks for them to run on.” Joy Weiss of Linear Technology discussed the unique performance requirements of in-plant wireless sensor networks.

Generally speaking, the Internet of Things (IoT) is built on the promise of increasingly inexpensive sensors that automatically plug into a cloud of ubiquitous connectivity. But in a steel mill, chemical plant or oil refinery, not only are conditions harsh and potentially dangerous, electrical power often is not available, radio frequency interferences are rife, and, once in place, sensors typically are expected to operate reliably for years at a stretch with little or no attention from plant maintenance staff.

What’s needed in this context are robust, low power wireless networks that can run for years on battery power yet overcome the many interferences inherent in a plant environment, according to Joy Weiss, president of Linear Technology’s Dust Networks product group, who discussed the particular requirements of in-plant wireless sensor networks at the Smart Industry 2015 conference in Chicago.

According to Weiss, reliability and security are plant managers’ top concerns when it comes to implementing wireless sensor networks. Reliability, in particular, depends on network architecture and arises from the appropriate amount of redundancy in both path and channel. Mesh networks are designed to allow signals to follow a variety of paths, hopping from one node to another and among channels as well. Achieving security in industrial wireless networks requires lot of careful engineering, but established protocols such as WirelessHART have been put through the paces with embedded security from the edge of the network back to the head, Weiss said. “By design, protocols such as WirelessHART mitigate the most common kind of known security issues.”

Network synchronization is also important for transmission reliability, since it decrease the possibility of packet collisions, Weiss added. “Synchronized networks minimize the possibility of self-interference and, by eliminating retries, allow lower power consumption across the network.” This also allows every packet to be time stamped, which can add critical data to your analysis because you can sequence events that have happened, she said.

Networking for non-experts

Further, industrial wireless networks typically are not installed by wireless experts, Weiss cautioned. “So you need to have products that can be installed as simply as wired products or products that have no communication capability. Their networks need to be self-forming, self-healing and self-maintaining. “You need to make sure that when you deploy a network, its relative health is easy for an installer to know before they leave the site,” Weiss said. “It has to be done quickly, and there has to be an indicator that says, ‘you’re good to go’.”

And if things aren’t running properly you need to know and you need to know where the problem is. Having a network that is instrumented to provide that visibility is critically important. The right software should provide excellent visual capabilities for non-experts to see if and where there may be a problem so you can remedy the problem very quickly. One key area is visibility into battery life so you can schedule battery replacement, even years in the future, wherever that sensor may be.

In-plant wireless networks need to be able to self-form, self-heal, self-monitor, self-optimize, self-configure and self-diagnose, Weiss said in conclusion. “They need to be highly configurable because some applications may require data once a day while others require data once an hour or once every 10 seconds,” she said. “If we’re going to have smart things, then we need smart networks for them to run on.”